Liquid level gauge



51953 A. s. GRIFF!TH, JR 2,649,714

LIQUID LEvEL GAUGE Filed Dec. 20, 1951 2 Sheets-Sheet 1 IN V EN TOR.

AndrewSGmjfithJr,

A TTORNE Y.

25, 1953 A. s. GRIFFITH, JR 2,649,714

LIQUID LEVEL GAUGE 7 Filed Dec. 20, 1951' 2 Sheets-Sheet 2 IN VEN TOR:

x l ndrewS. Grfitk fn 7,450 51. 711 (2,2

A TTORNEY.

Patented Aug. 25, 1953 UNITED STATES PATENT OFFICE r 'uqum ifizxifcaueu 7 Andrew S. Griffith, Jr., Waynesboro, Va., assignor to E. I. du Pont de Nemours & Company, Wilmington, Del.,a corporation of Delaware Application December 20, 1951, Serial No. 262,550 3 Claims. (01. 73--299) This invention relates to improvements in liquid level gages and particularly to liquid level gages of the force-balanced diaphragm type, such as those used for the measurement of the levels of liquids stored at subatmospheric pressures, or under pressures which may vary over a relatively wide range from subatmospheric to considerably above atmospheric pressure.

Force-balanced, diaphragm type liquid level gages have hitherto been employed for the sensing of differential pressures wherein the lower limit of the range is below the atmospheric pressure level, however, measurement has been effected at the same relatively low absolute pressures. This has been disadvantageous, because of the small flows of air required for counterbalancing and the criticality of the sizes of the orifices which must necessarily be employed, both from the standpoint of fabrication and adjustability. This disadvantage becomes progressively more serious as the absolut ambient pressure of the system to be evaluated decreases until, in situations corresponding to that in which it is desired to measure levels of below about 40 in. of water under absolute pressures of 10-20 mm. Hg by pressure differential, conventional gages become entirely unreliable.

It is a primary object of this invention to provide a force-balanced, diaphragm type liquid level gage wherein measurement can be accomplished at superatmospheric pressure.

It is another object of this invention to provide a force-balanced, diaphragm type liquid level gage having few parts, and which is economical in first cost and maintenance.

Another object of this invention is to provide a force-balanced, diaphragm type liquid level gage having low inertia characteristics and therefore a high sensitivity of response.

Another object of this invention is to'provide a force-balanced, diaphragm type liquid level gage adapted to use with viscous or polymerizable liquids which has little dead space wherein the liquids can collect and thereby interfere with operation.

The manner in which thes and other objects are attained will become apparent from the following detailed description and the accompanying drawings, in which: V

Fig. 1 is a sectional side elevational view of one embodiment of this invention utilized for the measurement of the level of a liquid within a tank, the interior of which is maintained at an absolute pressure of the order of 20 mm; Hg or lower, or wherein the ambient pressure is variable between this and higher levels, a v

. 2 r Fig. 2- is a full sectional view of the apparatu taken along line 22 of Fig. 1,

Fig. 3 is an end elevational view of the apparatus looking in the direction of the liquid storage tank to which it is attached,

Fig. 4 is a detail view of a preferred embodi ment of sensing diaphragm having an abutting connection with the transmitter mechanism.

Generally, the objects of this invention are accomplished by providing a sensing diaphragm in direct contact with the liquid measured against which the pressure of the liquid is applied and communicating this pressure to a multiple diaphragm transmitter, which compensates for the lowest pressure of the system and is at the same time opposed by the balancing pressure of an indicating system operating above atmospheric level.

Referring to Fig. 1, the gage assembly is attached to the tank wall H1 in fluid-tight relationship by bolts l2 engaging with blind tapped holes in the tank wall. When the gage is mounted on the side wall it is preferred to locate it as close to the bottom of the tank as practicable,

so that the sensingdiaphragm I3 will be below the level of the'liquid for all depths which it is desired to measure. Mounting on the side of the tank hasthe advantage that the gage is usually more accessible than if it is mounted on the bottom, however, there is no'reason why it cannot be mounted in the latter position if this is desired. When the gage is mounted on the bottom of a tank it will be understood that the weight of the elements supported by the diaphragms will introduce a zero shift into the readings which must be compensated for by adjustment of the zero point of the indicating instrument, or in other similar ways known to the art and therefore not further described herein.

The tank is provided with a circular port ll of the same size as the central opening of base ring 14, thus exposing diaphragm I3 to direct contact with the liquid contents of the tank. It is desirable to locate'diaphragm I3 as close to prolongation with the inside tank Wall as possible, particularly when viscous or polymerizable liquids are involved, to minimize the collection of material within port II which might otherwise cause spurious indications. This consideration usually favors side mounting of the gage, as opposed to bottom mounting, because the interior side walls of a tank can generally be cleaned more readily than the bottom and, also, settling results in the deposition of solids on the bottom surfaces between successive cleanings.

As best seen in Fig. l, the gage housing comprises externally recessed base ring I4, cylindrical side wall l5 and cap it, these elements being secured together as a unit by bolts [1 which engage with blind tapped holes in ring H. The outer periphery of diaphragm i3 is provided with holes mating with bolts H, to permit insertion of the bolts therethrough, andishe diaphragm is thus retained in a vertical plane by compression between ring 14 and side wall 15.

The central portion of diaphragm i3 is;

strengthened by washers i8 and is drilled to which is maintained by a constant differential receive machine screw 19, which is firmly secured to the diaphragm by nut 28.. The oppositezend of screw [9 is attached to spider '25 bypassage: through a hole in the central-portion. of the ..=l5

spider and retention by locknut 2! .Spider .25 may conveniently be of unitary construction;

with three equidistantly arranged armsrfiangedg I at the ends for screw attachment with the three similarly disposed arms of yoke 26, shown in plan in Fig. 2.

A- preferred construction for transmitting deflection of diaphragm I3 to spider obviating positive connection therebetween is shown in Fig.- 4. In this arrangement the pressure of the liquid applied to diaphragm [3 causes thediaphragm to abut against a knob 58, WhiCh'lS preferably fabricated from a substance light in weight, such as, a polymeric material, fixedly secured tothe end of screw l9. Elimination of a positive connection between diaphragmit and screw 19 in this manner has the advantages that assembly of the apparatu is simplified and there is less possibility of liquid leakage from the tank into the gage housing, due to the fact that the central area of i3 is not perforated.

A two-part sub-housing comprising a cylindrica-l side wall element 2? and an interior closure cap 28,'both secured to cap l6 by'bolts 29, supports the two diaphragms 3d and 3| in a vertical plane parallel to diaphragm 13. In this connection, diaphragm BI is provided with peripherally disposed holes mating with bolts 29 andflis. compressed in air-tight relationship between base cap 16 and side wall 2! so that it forms, with'cap 5, a chamber 32. Diaphragm30 is in all respects identical to Iii, except'that it is compressed between side wall 2? 'and'cap 28, thus defining chamber 33.

Diaphragms 3E and 3! are rigidly connected to each other and to the hub of yoke 26 .by halfspool separators 38,. disposed on adjacent. sides of the diaphragms, and gaskets 39 andidfl on the other sides thereof, gasket 5!; being provided with an integral threaded stem ll. passing .through central apertures in each of the recited elements in turn and carrying securing nut 42 at its remote end. A closure disc G3,.adaptedtothrottlethe flow of air through orifice 52 of bleed nozz1e53, is secured to the right-hand ide of gasket.

As is apparent from Fig. l, sub-housing sidewall 21 is provided with slots 45% of sufiicient. width to permit free horizontal movement of yoke 26 in response to movements of diaphragmv l3, to which ZEis attached by spider 25. At thesame time slots it establish open communication between the interior of the centralchamberof the sub-housing and the interior of the gage housing, thus insuring maintenanceof the same pressure in both enclosures at all times. This pressureds made equal to the absolutepressure maintained over the liquid stored inthe 'tank'by connecting the interior of the gagehousing to a pointin the tank above the maximum'liquid filling level through-line 45;

Chamber 33, of which diaphragm 39 constitutes one wall is vented to the atmosphere, which may be conveniently accomplished by providing a passage 66 in communication with a through-going drilled passage 4! extending the full length of bolt 29', or by other suitable means. Chamber 32, through 1 which the-balancing pressure is applied, issupplied with air at superatmospheric pressure by line 48 which is connected with line 49;. The supply of air is at a constant flow rate,

fiow-controller 5|, such as the Model 63BU design inarketedby the Moore Products Co. and shown in; its Bulletin .60jl;. The air supplied to controller 5l-issderivedfromwa conventional constant pressure source, not shown, which is preselected to maintaima-pressure"level several pounds higher thar-r thezmaximum liquid head pressure which the gage is intended to measure. A standard indicating-recordinginstrument 53, which may be calibrated to read directly in terms of liquid level, is also connected in line 153; Air discharging from chamber 32 as a result of the throttling action of. disc 43 on orifice .52 passes into the atmosphere through the exterior opening 54 of bleed nozzle 53..

In operation, air is supplied to chamber 32 from line 49 and its associated flow controller 5| at a predetermined flow. rate which develops a pressure in chamber 32 .sufiicient to overcome the maximum head of liquid which is to be stored in the. tank. One. commonly used design of indicator-recorder 53 has anoperating pressure range-of 3 to 18 lbs/sq. in., therefore, a maximum pressure just below. l8'1bs.'gage may be adopted as the upperdatum level. By proportioning the areas of diaphragms 3d and! in. the proper ratio to thearea of diaphragm l3,- it. will beunderstood thata relatively .widerange of liquidlevels may be measuredbythe device of this invention whilestill using a- 3-18 lb. range indicatorrecorder.

The head of liquid confined in the tank exerts a pressure on diaphragm IS which is proportional to the height existing above the diaphragm. Where the gage is mountedon the tanlr side wall, as hereinabovedescribed, it is preferred to limit measurementsby indicator-recorder til to the determination of liquid levels above port H, so that the ambient pressurein chamber 32' is always appreciably. above atmospheric Such a practice also eliminates any error which might result from only partialsubmersion of diaphragm i3. Where the gage-isused in this manner, in dicator-recorder can either-be calibrated to include the head below the upper edge of H as. an invariable factor, or the zero point of the scale of 5i) may be taken as located here andthe residual material in thetank ignored for purposes of gaging, whichever is desired.

Analysisaof the forces acting .onthe several diaphragms ofdifferential: gages constructed ac cording. to ,this invention shows that the net eifective force transmitted to the left side of diaphragm M is equalto-thatof the head of liquid confined inthe-storage tank solely. This condition is brought about bythe. pressure compensa tion effected by diaphragm lifi .(Fig, 1)., the right side of which is :under the same pressure as that existing abovethe. liquid by open connection with thetop of the tank through line lfi. To permit indication at superatmospheric pressures, it is necessarytoiadd a rightward-acting increment of force equal; to the prevailing atmospheric pressure, and thisis accomplished'by exposing the left side of diaphragm 3D to the atmosphere through drilled passage 41 of bolt 29'. The net effective pressure applied to diaphragm 30 is added to that derived from the combined spider-yoke mechanical connection with diaphragm I3 and is transmitted directly to the left side of diaphragm Bl through the spool-gasket connection hereinbefore described. This pressure urges closure disc 23 against orifice 52 of bleed nozzle 53 in opposition to the pressure of the balancing air supplied to the right side of diaphragm 3| through line 43. The net pressure transmitted to the left side of 3| is always less than the balancing pressure exerted against the right side, therefore, more or less air is permitted to escape to the atmosphere through bleed nozzle 53 and the ambient pressure in chamber 32, measured by indicator-recorder 5B, is a function of the liquid head pressure of the contents of the storage tank.

It will be understood that, while liquid level gages constructed according to this invention have particular utility in the measurement of levels of liquids which are stored under vacuum, or where the pressure over the liquids may occasionally fall from atmospheric or superatmospheric to subatmospheric levels, all of the advantages are retained even where operation is entirely within the superatmospheric range. In tests it has been determined that the gage possesses a substantially linear indication at all pressure levels and has a sensitivity greater than about 0.1" of water change in liquid level within the region just covering diaphragm l3 to 100" or more.

Many other changes and modifications within the spirit of this invention will occur to persons skilled in the art, wherefor it is desired to be limited only by the scope of the following claims.

What is claimed is:

1. A force-balanced liquid level gage comprising in combination a housing, a sensing diaphragm constituting one wall of said housing, a sub-housing disposed within said housing comprising a first chamber defined by a first diaphragm disposed parallel to said sensing diaphragm and a second chamber defined by a second diaphragm disposed parallel to said sensing diaphragm, the outside walls of said first and second diaphragms and the inside wall of said a sensing diaphragm being subjected to the pressure existing above the liquid measure and the inside wall of said first diaphragm being subjected to atmospheric pressure, a rigid mechanical connection between said first and second diaphragms, means transmitting forces acting on the outside surface of said sensing diaphragm to said rigid mechanical connection, a bleed nozzle connecting said second chamber with the atmosphere with its inlet disposed adjacent the inside wall of said second diaphragm whereby air flow through said nozzle is throttled by inward movement of said second diaphragm, means supplying balancing air to said second chamber at a substantially constant rate of flow and a predetermined pressure slightly greater than the maximum head of the liquid level which it is desired to measure, and means for indicating the pressure existing in said second chamber as a function of the existing liquid level.

2. A force-balanced liquid level gage comprising in combination a housing, a sensing diaphragm constituting one wall of said housing, a sub-housing enclosed within said housing and co-axial therewith, two transmitter diaphragms mounted within said sub-housing in parallel relationship with said sensing diaphragm, one transmitter diaphragm defining a first chamber adjacent said sensing diaphragm with one end of said sub-housing, the other transmitter diaphragm defining a second chamber with the opposite end of said sub-housing, and the space between said transmitter diaphragms being in open communication with the interior of said housing, a rigid mechanical connection between said two transmitter diaphragms, means transmitting forces acting on said sensing diaphragm in the direction of the interior of said housing to said rigid mechanical connection between said two transmitter diaphragms, an open fluid passage in said housing communicating with the space above the liquid measured, an open fluid passage connecting said first chamber with the atmosphere, a bleed nozzle connecting said second chamber with the atmosphere, a closure disc on the chamber side of the diaphragm defining said second chamber disposed to throttle the flow of air through said bleed nozzle, means supplying balancing air at a substantially constant rate of flow and a predetermined pressure slightly greater than the maximum head of the liquid level which it is desired to measure connected to said second chamber, means for indicating the pressure existing in said second chamber as a function of liquid level, and means for mounting said gage on the enclosure containing the liquid measured with said sensing diaphragm in direct contact with the liquid at the point wherein the maximum pressure of the range examined exists.

3. A force-balanced liquid level gage according to claim 1 wherein said means transmitting forces acting on the outside surface of said sensing diaphragm to said rigid mechanical connection comprises an abutment element attached to said rigid mechanical connection and disposed closely adjacent the inside wall of said sensing diaphragm, whereby movements of said sensing diaphragm are transmitted to said abutment element.

ANDREW S. GRIFFITH, J R.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,418,614 Annin Apr, 8, 1947 2,467,365 Annin Apr. 19, 1949 2,520,547 Hughes Aug. 29, 1950 2,584,455 Hughes Feb. 5, 1952 

